How to write query to select first event forever that matches given criteria

Question

I have stream of events like "page view" - pageUrl - timestamp - ...

I need to select only "first" page view event for each pageUrl. I know about ISFIRST but AFAIU it accepts time window as a mandatory parameter, but I need to filter first event "forever"

Answer 1

it accepts time window as a mandatory parameter

Yes, time window is required because all the aggregate function need a set of data during a period of time.

SELECT 
    pageUrl,
    timestamp
INTO
    MyOutput
FROM 
    Input TIMESTAMP BY Time
WHERE 
    IsFirst(minute, 60) OVER (PARTITION BY pageUrl) = 1

I suggest you create a job to query the first event for a period of time and export the data. You could query the exported data(MyOutput) to get the first page view event for each page URL.